The invention pertains to a spiral-line press for the extruding of thermo-plastic synthetics in a reciprocally conveying co-axial construction with two feeding sources. It pertains to a construction of the spiral geometry in such a way that the space requirement can be reduced and the operation be less expensive.
Spiral-line presses have become known which were cut on one shaft and which had reciprocally conveying canals of cochlea in which the compensation of the longitudinal forces was the main factor, especially in double and multiple spirals, in which the housing for the axial bearing is complex.
These constructions have, until today, not reached any special importance, since the advantages of an axial bearing simplification are generally offset by an increased expenditure for the operation.
In the conventional spiral-line presses of today the usual ratios of spiral length to spiral diameter are between 20/1 and 30/1. This means, in a reciprocal conveying arrangement of two spirals on one shaft a combined length of 40/1 to 60/1. For spirals of such lengths, a one-sided operation is no more feasible, since the force for the operational shaft would surpass the permissible dexterity values in performances as are nowadays required. One must, therefore, operate from two sides, and thereby the advantage of a cheaper axial bearing is offset.
To fully utilize the advantages of the axial power compensation, the reciprocally conveying spirals are, based on the presented proposal, constructed at a total length of a maximum of 28/1 and with a canal of cochlea depth in the metering zones of 1/25 of the spiral diameter.
Thereby, the polar resistance moment of the input shaft is, at one side of the shaft, sufficient to operate the spirals. Preferably one should apply the spiral geometry of fast-running, adiabatically working spiral-line presses (See "Optimal Measurings of Fast-running Extruder Spirals, Synthetics Journal Year 1963, Edition 10.) (German Title: Optimale Abmessungen von schnelllaufenden Extruderschnecken", Zeitschrift Kunststoffe, Jahrgang 1963, Heft 10).)
Fast-running autogenous or adiabatic spiral presses can only be used successfully, if the ratio of longitude to diameter L/D .ltoreq. 14/1 is not exceeded, thereby, in an arrangement of two spirals on one shaft, the condition L/D .ltoreq. 28/1 results. An autogenous or adiabatic operational manner is, in short spirals of L/D .ltoreq. 14/1, only possible with flat gears in the metering zone and peripheral velocities of more than 0.3 m/sec. The savings in the longitudinal bearing can only be utilized to its fullest extent, if the two spiral presses which are on one shaft do not exceed a total length of L/D .ltoreq. 28/1, since the required operational capacity for the two spirals can be applied from one side only below this limit.
It is possible, in adherence to the measures proposed in this invention, to operate one spiral press in counterarrangement with one shaft and thereby to utilize the simplification of the savings in the bearing. A combination of the characteristics L/D ratio with the phase depth in the metering zone and the peripheral velocity lead to a progressive effect; this is the essence of the presented invention.
Based on the formula of the presented invention, the two flows of matter which are moving towards each other are guided out of the extruder by a shaped part in vertical axial direction in a manner that the matter flowing from the one side, with a circular cross-section in the center, and the flow of matter on the other side around the circular cross-section, exits in orbicular cross-section. This construction type in the invention as presented serves the circular distribution of the two flows of matter, it can be simultaneously applied if the flows of matter consist of different materials.
A circular distribution is required because the two flows of matter, even if the same materials are processed, can show small viscosity differences as the result of processing tolerances of spirals and boxes.
Another possibility to equalize differences in the two product flows consist in the after-switching of a known static mixing device.